1. Field of the Invention
The present invention relates to a method for forming a fine resist pattern, and more particularly to a method for forming a fine resist pattern utilizing a phase-shifting effect in the fabrication of a semiconductor device.
2. Description of the Invention
An attention is given to a method for forming a fine pattern exceeding the resolution limit of a reduction projection aligner, namely stepper which utilizes a phase-shifting effect usually on a mask.
There is also proposed a method for forming a fine pattern utilizing a phase-shifting effect on a semiconductor substrate (IEDM 91, pase 63-66 and U.S. Ser. No. 874,809, filed Apr. 28, 1992, now U.S. Pat. No. 5,330,862). This method involves forming a resist layer on a semiconductor substrate; forming a phase-shifting pattern in an upper portion of the resist layer; exposing the surface of the semiconductor substrate including the phase-shifting pattern; and forming a fine resist pattern below the edge of the phase-shifting pattern.
Hereinbelow is described a method for forming a fine resist pattern by providing a phase-shifting pattern on a single layered resist surface using a phase-shifting effect on a semiconductor substrate.
As shown in FIG. 15, a positive type resist is applied on a silicon substrate 41 with the spin-on method, and then prebaked to form a resist layer 42, followed by subjecting the surface of the resist layer 42 to exposure using a mask 43.
The resist layer 42 is taken baked and developed to form a phase-sifting pattern 42a as a projecting portion 44, as shown in FIG. 16. The thickness Ts of the phase-shifting pattern 42a is identical to the height thereof in the direction perpendicular to the surface of the projecting portion 44 (in the direction of an arrow designated by Symbol H in FIG. 16). Subsequently, the entire surface of the resist layer 42 including the phase-sifting pattern 42a is exposed, where the phase of light passing through the phase-shifting pattern 42a is almost reversed to the phase of light passing through a recessed portion 45 sandwiched between the projecting portion 44. This means that the optical amplitudes of the two lights are offset each other in a lower region L at the edge E of the phase-shifting pattern 42a, whereby the light intensity becomes zero. Consequently, the lower region L at the edge E of the phase-shifting pattern 42a is not exposed, so that the fine resist pattern 46 is formed after the development as shown in FIG. 17.
In the above method, a mask 43 shown in FIG. 18 is used to expose the resist layer 42, thereby forming a phase-shifting pattern 42a. Thereafter, exposing over the entire surface of the resist layer 42 including the phase-shifting pattern 42a results in the mutual offset of the phase of light passing through the phase-shifting pattern 42a as a projecting portion 44 in FIG. 19 with the phase of light passing through the recessed portion 45. Thus, the lower region L at the edge E of the phase-shifting pattern 42a is not exposed, thereby forming a fine resist pattern 46 shown in FIG. 20 after development.
However, there occurs a problem that a short circuit is generated as shown by 46E in FIG. 20 because a similar effect is generated at an edge portion Eb in the longitudinal direction of the phase-shifting pattern 42a as shown in FIG. 19.
Furthermore, the above method is not appropriate to form a different pattern having a large pattern such as pads or the like and a fine pattern.